The invention relates to a radiation-sensitive semiconductor device comprising a semiconductor body which provided with at least two sub-elements on a substantially plane surface, which subelements constitute radiation-sensitive diodes with the adjoining parts of the semiconductor body, the distance between the subelements being small enough to enable the zone of the semiconductor body between the subelements to be depleted completely by the depletion regions associated with the subelements by applying a reverse voltage across the diodes, so as to inhibit charge transfer between the subelements and a circuit for applying reverse voltage across the radiation-sensitive diodes and for detecting the photoelectric currents generated by the radiation in & the radiation-sensitive areas of the diodes constituted by the depletion regions.
Radiation-sensitive semiconductor devices of the above type are employed, for example, in light-sensitive circuit arrangements for image reproduction and in apparatuses for tracking or positioning light beams (or beams of radiation of a different kind). Other uses of radiation detection lie in the field of spectroscopic analysis, in particular in the waverange from 200-1100 nanometers and, for example, soft X-rays. More& over, such devices are employed for the detection of corpuscular radiation (for example electrons, .alpha.-particles or high-energy particles). Further, such semiconductor devices (specifically in the waverange of visible light) are utilized in measuring equipment for positioning detection, for example for flexure measurement, or for example in automatic assembly lines.
The invention further relates to a focus-error detection system equipped with such a semiconductor device and to an apparatus for reading and/or recording information in a radiation-recording surface of a record carrier, which apparatus is equipped with such a focus-error detection system.
A semiconductor device of the type defined above the opening paragraph is known from Netherlands Patent Application no. 8003906 laid open to public inspection on the Feb. 1, 1982, corresponding to U.S. patent application Ser. No. 153,523. Said application describes a quadrant diode, comprising four radiation-sensitive diodes which are arranged symmetrically relative to a common center. When the quadrant diode is exposed to a beam of radiation, currents are generated in the four diodes, the magnitude of each diode current being dependent upon the amount of radiation incident on the radiation sensitive area of the relevant diode. The differences between the diode currents are representative of the position where the radiation beam is incident on the quadrant diode relative to the common center. The above Patent Application also describes a focus-error detection system which utilizes the quadrant diode for the purpose of detecting a deviation between a radiation-reflecting or first plane and a focussing or second plane of an objective system (for example for use in a Compact-Disc or video-disc apparatus). The known quadrant diode is very fast and has a high resolution and a high radiation sensitivity, but during assembly the diode has to be mounted in such a way that in the case of a correct focussing the radiation beam is incident on the semiconductor surface exactly centered relative to the four quadrants of the diode. In view of the required tolerances (the quadrants are spaced approximately 5 micrometers from one another) such an assembly procedure with the corresponding alignment is difficult and time-consuming.
Similar assembly problems occur in a focus-error detection system in which in the path of the beam reflected from the radiation-reflecting surface a beam-splitting element is arranged, followed by a radiation-sensitive detection system comprising a plurality of detectors which are spaced from each other by narrow strips, the subbeams formed by the beam-splitting element being incident on the separating strips. In the last-mentioned case it is possible to ensure that the centers of the radiation spots formed in the detector plane by the subbeams are situated on the separating strips in the case of a correct focussing by arranging these strips at an acute angle to one another. By mechanically shifting the detector plane a correct preliminary adjustment can be obtained, as is described in more detail in Netherlands Patent Application no. 8202058, corresponding to U.S. Pat. No. 4,533,826. However, this mechanical adjustment may vary with time and/or temperature, necessitating an often tedious readjustment of the detector plane.